Block $\displaystyle {A}$ hangs from a light string that passes over a light pulley and is attached to block $\displaystyle {B}$, which is on a level horizontal frictionless table, as shown above. Students are to determine the mass of block $\displaystyle {B}$ from the motion of the two-block system after it is released from rest. The students must also take which of the following measurements to determine the mass of block $\displaystyle {B}$? Select all that apply.